How to Dilute and Store Sulphuric Acid Safely: Dilution Chart, Density and Tank Materials

Most industrial sulphuric acid is shipped at 98%, the strongest ordinary grade. It is the cheapest way to move the acid, because you pay to ship H₂SO₄ rather than water. But many processes run on weaker acid: 70% for fertilizers, around 37% for batteries, 10–25% for metal pickling and pH control. So buyers dilute on site.

Diluting and storing sulphuric acid is simple if you follow a few rules, and dangerous if you don't. This guide gives a dilution chart for 98% acid, the density of each strength, the right tank materials, and the mistakes to avoid. The figures are based on the sulphuric acid 98% we supply.

Our sulphuric acid 98% at a glance

Property	Value
Purity	Min. 98.0% (recent lot: 98.0%+)
Specific gravity at 20 °C	1.82 – 1.84 (recent lot: 1.83)
Iron (as Fe)	Max. 20 ppm (recent lot: 12 ppm)
Packing	1,650 kg IBCs (about 900 litres), drums or tankers
UN number	UN 1830, Class 8 (corrosive), Packing Group II

For the full COA results and supply details, see Sulphuric acid 98%: specifications, COA results and supply near Mundra Port.

The golden rule: always add acid to water

Always add the acid slowly to the water, never water to the acid.

Mixing sulphuric acid with water releases a lot of heat. If you pour water into concentrated acid, the first water to arrive boils on contact and throws out hot acid. If you add acid to a larger amount of water, the water absorbs the heat safely.

In practice:

1. Put the full amount of water in the tank first, using cold water.
2. Add the acid slowly in a thin stream, with continuous stirring or circulation.
3. Watch the temperature. Pause, or cool the tank, if it gets hot. Large batches need a cooling coil or jacket.
4. Let the solution cool before closing the tank or using it.

Dilution chart: making weaker acid from 98%

To make 100 kg of diluted acid from 98% sulphuric acid:

Target strength	98% acid (kg)	98% acid (litres)	Water (kg or litres)
93%	94.9 kg	51.7 L	5.1
70%	71.4 kg	38.9 L	28.6
50%	51.0 kg	27.8 L	49.0
37% (battery strength)	37.8 kg	20.6 L	62.2
25%	25.5 kg	13.9 L	74.5
10%	10.2 kg	5.6 L	89.8

The litres of acid are based on a density of 1.836 kg/L for 98% acid. For any other strength:

kg of 98% acid = (target % ÷ 98) × kg of solution you want, and the rest is water.

Always weigh where you can. Measuring by volume is less accurate, because the solution shrinks a little as the acid and water mix.

Density by strength

Density, or specific gravity, is the quickest check on a diluted batch. Standard values at 20 °C:

H₂SO₄ strength	Specific gravity (kg/L)	Litres per tonne
98%	1.836	545
96%	1.835	545
90%	1.814	551
80%	1.727	579
70%	1.611	621
60%	1.498	668
50%	1.395	717
40%	1.303	767
35%	1.260	794
20%	1.139	878
10%	1.066	938

Why density alone can't confirm 98%

Density is useful for dilute acid, but not for telling 93% from 98%. The density of sulphuric acid peaks at around 97–98% and hardly changes between 93% and 99%. A specific gravity of 1.83 fits our 98% acid, and it would also fit 93% acid. That is why the purity on a COA is measured by titration, not by density. Check the purity figure on the COA, not just the specific gravity.

Which strength is used for what?

Strength	Common uses
98%	Chemical manufacturing, alum and sulphate salts, fertilizers, drying gases
93% (66 °Bé)	Fertilizers and chemicals; stays liquid in cold weather
70 – 80%	Single superphosphate (SSP) fertilizer production
50%	pH control, chemical processing
35 – 40%	Lead-acid battery electrolyte (battery grade)
10 – 25%	Steel pickling, pH adjustment, cleaning

Storage: choosing the right tank material

Concentrated and dilute sulphuric acid behave very differently, so the tank material has to match the strength:

Strength	Suitable	Avoid
93 – 99%	Carbon steel tanks (the standard for bulk storage), stainless steel; HDPE IBCs and drums for transport at ambient temperature	Letting water or moist air in: diluted acid attacks steel
80 – 93%	Stainless steel, lined steel; ask for a material check	Plain carbon steel at higher temperatures
Below about 80%	HDPE, polypropylene, FRP (vinyl ester), PVDF, rubber-lined or PTFE-lined steel	Carbon steel, which corrodes quickly at these strengths

Strong acid forms a protective iron sulphate layer on carbon steel, which is why steel tanks work for 98% acid. Once the acid is diluted, that layer dissolves and the steel corrodes fast, giving off flammable hydrogen gas. So:

• Never store diluted acid in a tank built for 98%.
• Keep concentrated-acid tanks dry. Fit a desiccant breather on the vent so moist air can't dilute the acid at the surface.
• Vent steel tanks and keep sparks and flames away, because of the hydrogen risk.
• Give every tank secondary containment (a bund) that holds at least the full tank volume, lined with acid-resistant material.
• Label tanks and pipes with the strength and the corrosive hazard sign.

Watch out for freezing in cold climates

Sulphuric acid 98% freezes at only a few degrees above 0 °C, so tanks and pipelines exposed to winter weather can freeze. Acid at 93% (66 °Bé) stays liquid down to well below −30 °C, which is why it is preferred in cold regions. If you store 98% acid outdoors in winter, insulate or heat-trace the tanks and lines, or plan to dilute to 93% on arrival.

Battery acid is a different grade

Battery electrolyte is diluted to about 35–38% (specific gravity around 1.26–1.28) with demineralised water. It must be made from battery-grade acid, with tighter limits on iron and other metals than industrial acid. Our industrial grade is not sold as battery acid. Tell us your specification and we will confirm availability.

Safety essentials

• Wear protective equipment when diluting: chemical goggles with a face shield, acid-resistant (neoprene) gloves, an acid-resistant apron and boots.
• Keep a safety shower and eyewash station next to the dilution area.
• Skin or eye contact: flush with running water for at least 20 minutes and get medical help immediately.
• Spills: contain with dry sand or earth, not water, then neutralise the residue with soda ash or lime.

The full safety data sheet comes with every order. Read our guide to what to check in an SDS.

Request a quote

We supply sulphuric acid 98% in 1,650 kg IBCs, drums or tankers, with a COA for every lot. To get a price, send us:

1. Quantity, and whether it is a one-time or a regular requirement
2. Packing: tanker, IBCs, drums or carboys
3. Delivery location, or your destination port
4. The strength you use on site, if you'd like advice on dilution or storage

See the Sulphuric Acid product page or contact us for a quote.